[llvm] r184592 - Improve the time it takes to generating dwarf for assembly source files

[Eric Christopher]

> comment.  And the current code calls SrcMgr.FindLineNumber()
> twice to do this causing its cache not to work and results in very
> slow compile times:
>
> % time /Volumes/SandBox/build-llvm/Debug+Asserts/bin/llvm-mc -triple thumbv7-apple-ios -filetype=obj -o /tmp/x.o mscorlib.dll.E -g
> 672.542u 0.299s 11:13.15 99.9%  0+0k 0+2io 2106pf+0w
>
> So we save the info from the last parsed cpp hash file line comment
> to avoid making the second call to SrcMgr.FindLineNumber() most times
> and end up with compile times like:
>
> % time /Volumes/SandBox/build-llvm/Debug+Asserts/bin/llvm-mc -triple thumbv7-apple-ios -filetype=obj -o /tmp/x.o mscorlib.dll.E -g
> 3.404u 0.104s 0:03.80 92.1%     0+0k 0+3io 2105pf+0w
>

*blink* 11 minutes to 3 seconds? Nice work :)

-eric

> rdar://14156934
>
> Modified:
>     llvm/trunk/lib/MC/MCParser/AsmParser.cpp
>
> Modified: llvm/trunk/lib/MC/MCParser/AsmParser.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCParser/AsmParser.cpp?rev=184592&r1=184591&r2=184592&view=diff
> ==============================================================================
> --- llvm/trunk/lib/MC/MCParser/AsmParser.cpp (original)
> +++ llvm/trunk/lib/MC/MCParser/AsmParser.cpp Fri Jun 21 15:51:39 2013
> @@ -160,6 +160,13 @@ private:
>    int64_t CppHashLineNumber;
>    SMLoc CppHashLoc;
>    int CppHashBuf;
> +  /// When generating dwarf for assembly source files we need to calculate the
> +  /// logical line number based on the last parsed cpp hash file line comment
> +  /// and current line. Since this is slow and messes up the SourceMgr's
> +  /// cache we save the last info we queried with SrcMgr.FindLineNumber().
> +  SMLoc LastQueryIDLoc;
> +  int LastQueryBuffer;
> +  unsigned LastQueryLine;
>
>    /// AssemblerDialect. ~OU means unset value and use value provided by MAI.
>    unsigned AssemblerDialect;
> @@ -1519,7 +1526,18 @@ bool AsmParser::ParseStatement(ParseStat
>          getStreamer().EmitDwarfFileDirective(
>            getContext().nextGenDwarfFileNumber(), StringRef(), CppHashFilename);
>
> -       unsigned CppHashLocLineNo = SrcMgr.FindLineNumber(CppHashLoc,CppHashBuf);
> +       // Since SrcMgr.FindLineNumber() is slow and messes up the SourceMgr's
> +       // cache with the different Loc from the call above we save the last
> +       // info we queried here with SrcMgr.FindLineNumber().
> +       unsigned CppHashLocLineNo;
> +       if (LastQueryIDLoc == CppHashLoc && LastQueryBuffer == CppHashBuf)
> +         CppHashLocLineNo = LastQueryLine;
> +       else {
> +         CppHashLocLineNo = SrcMgr.FindLineNumber(CppHashLoc, CppHashBuf);
> +         LastQueryLine = CppHashLocLineNo;
> +         LastQueryIDLoc = CppHashLoc;
> +         LastQueryBuffer = CppHashBuf;
> +       }
>         Line = CppHashLineNumber - 1 + (Line - CppHashLocLineNo);
>      }
>
>
>
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